a list of the selected indices (0 for first) whenever the listbox is clicked

scale

value

whenever the value is changed, called with the new value

spinbox

value

whenever the value of the spinbox is changed by the buttons, the new one is returned

With the command property a function for handling the default event type of
widgets can be specified. This can be done with the :command initarg or
the command accessor (settable) for those widgets. The widgets that support
the command property are listed in table 2. The first
column lists the widgets, the second which arguments the function is passed (if any)
and the third one gives a brief description about when the event happens and what
the arguments contain.